PNNL

Abstract

The determination of the thermal and irradiation creep properties of V-4Cr-4Ti using the pressurized tube technique requires a supply of 4.57mm outside diameter tubing with a wall thickness of 0.250mm. Because of the high solubility and rapid mobility of oxygen in this material, maintaining the desired chemical and microstructural characteristics of the alloy during the fabrication of thin wall tubing presents a difficult technological challenge. In 1995, the US fusion program procured some 6 meters of tubing, using the US heat No.832665, utilizing commercial vendors [1].This effort, (Batch A), met with mixed success since a large fraction of the tubing developed cracks at both surfaces and during processing, the carbon concentration increased from 80 to 300wppm, oxygen increased from 310 to 700wppm, while nitrogen remained fairly constant. During the intermediate annealing cycles at 1000C for this batch the furnace vacuum was maintained in the 10-4 torr. range. In an effort to control oxygen pick-up during the intermediate annealing heat treatments, further processing of thin-wall tubing has been undertaken utilizing vacuum conditions in the 10-5 torr regime and in the 10-7 torr regime.